Belt retractors having force limiters are known from the prior art. The force limiter serves to limit the maximum forces acting in the seat belt in particular in case of an accident such that injuries of a restrained vehicle occupant are precluded. The limitation of the force is achieved by the fact that a rotation of the belt reel is permitted in order to unwind belt webbing when a certain belt webbing force is exceeded so that the force acting on the vehicle occupant is reduced.
A known structure of a force limiter uses a torsion bar which is connected at one end to a belt reel and is supported at the other end by a frame of the belt retractor. As soon as the torque acting on the belt reel due to the tensile forces acting in the belt webbing exceeds the resistance to torsion of the torsion bar, the torsion bar is twisted so that a rotation of the belt reel in the direction of belt webbing withdrawal takes place and thus the withdrawal of belt webbing is possible.
It is basically desirable to have a switchable force limiter. In this way, a strong belt webbing force can be used in a first condition, for example before a contact between a gas bag and the upper part of the body of the vehicle occupant, and a small belt webbing force can be permitted in a second condition, for example when the upper part of the body of the vehicle occupant is supported by the air bag.
The object of the invention is to provide a belt retractor for a vehicle occupant seat belt which is space-saving and permits different force limitation levels.